For an aircraft, the in-flight formation of ice on the external surface of the aircraft is undesirable. The ice destroys the smooth flow of air over the aircraft surface, increases drag and decreases the ability of an aerofoil to perform its intended function.
Also, built-up ice may impede the movement of a movable control surface such as a wing slat or flap. Ice which has built up on an engine air inlet may be suddenly shed in large chunks which are ingested into the engine and cause damage.
It is therefore common for aircraft, and particularly commercial aircraft, to incorporate an ice protection system. A commercial aircraft may use a system which involves bleeding hot air off from the engines, and the hot air is then ducted to the airframe components such as the leading edges of the wing and the tail which are prone to ice formation. More recently, electrically powered systems have been proposed, such as in EP-A-1,757,519 (GKN Aerospace) which discloses a wing slat having a nose skin which incorporates an electrothermal heater blanket or mat. The heater mat is bonded to the rear surface of a metallic erosion shield which comprises the forwardly-facing external surface of the nose skin.
The heater mat is of the “Spraymat” (trade mark) type and is a laminated product comprising dielectric layers made of preimpregnated glass fibre cloth and a heater element formed by flame spraying a metal layer onto one of the dielectric layers. The “Spraymat” has a long history from its original development in the 1950s by D. Napier & Sons Limited (see their GB-833,675 relating to electrical de-icing or anti-icing apparatus for an aircraft) through to its subsequent use by GKN Aerospace.
A recent “Spraymat” produced by GKN Aerospace for use in a wing slat is formed on a male tool and involves laying up a stack of plies comprising (i) about 10 layers of glass fibre fabric preimpregnated with epoxy cured in an autoclave, (ii) a conductive metal layer (the heater element) which has been flame sprayed onto the laminate using a mask to form the heater element pattern and (iii) a final 3 or so layers of the glass fibre fabric. Wiring is soldered to the heater element to permit connection to the aircraft's power system. The heater mat is then cured in an autoclave.
A heater mat often incorporates a metal connection that extends through several dielectric layers and several conductive layers such as the heater element and a terminal at the end of the wiring in order to connect the heater element to the wiring. The metal connection is a separate element which is thick and bulky. The heterogeneous nature of the metal connection relative to the surrounding components such as the dielectric layers induces thermal and mechanical stresses in the heater mat which can result in fatigue failure.
It would be desirable to provide an improved dielectric component with electrical connection, suitable for use in a heater mat or generally in any laminated product.